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<h1>The callback example</h1>
<center>
<img src="../images/callback.jpg" width="330" height="228" alt="callback"/>
</center>
<p>
Using the Qt signal-slot mechanism to connect a QGLViewer to your scene.
</p>
<p>
This very simple application uses the Qt signal-slot callback mechanism to link the QGLViewer and
your Scene. The two class hence remain totally independent. The <code>drawNeeded()</code>
QGLViewer signal is connected to the Scene <code>drawScene()</code> slot.
</p>
<h2>callback.h</h2>
<pre>
#include <qobject.h>
class QGLViewer;
// The Scene class must derive from QObject in order to allow a
// signal slot mechanism.
class Scene : public QObject {
Q_OBJECT
public:
Scene(const QGLViewer *const v);
public Q_SLOTS:
void draw();
};
</pre>
<h2>callback.cpp</h2>
<pre>
#include "callback.h"
#include <QGLViewer/qglviewer.h>
#include <math.h>
Scene::Scene(const QGLViewer *const v) {
// Connect the viewer signal to our draw slot.
connect(v, SIGNAL(drawNeeded()), this, SLOT(draw()));
}
// Draws a spiral
void Scene::draw() {
const float nbSteps = 200.0;
glBegin(GL_QUAD_STRIP);
for (float i = 0; i < nbSteps; ++i) {
float ratio = i / nbSteps;
float angle = 21.0 * ratio;
float c = cos(angle);
float s = sin(angle);
float r1 = 1.0 - 0.8 * ratio;
float r2 = 0.8 - 0.8 * ratio;
float alt = ratio - 0.5;
const float nor = .5;
const float up = sqrt(1.0 - nor * nor);
glColor3f(1.0 - ratio, 0.2f, ratio);
glNormal3f(nor * c, up, nor * s);
glVertex3f(r1 * c, alt, r1 * s);
glVertex3f(r2 * c, alt + 0.05, r2 * s);
}
glEnd();
}
</pre>
<h2>main.cpp</h2>
<pre>
#include "callback.h"
#include <QGLViewer/qglviewer.h>
#include <qapplication.h>
#include <qmessagebox.h>
using namespace std;
void help() {
QString text("<h2>C a l l b a c k</h2>");
text += "This example is conceptually the same as simpleViewer.<br>";
text += "The difference is that it uses the Qt signal/slot mechanism ";
text += "instead of deriving the QGLViewer class. ";
text += "The QGLViewer::drawNeeded() signal is connected to the "
"Scene::draw() method. ";
text += "The two classes are otherwise completely independant.";
QMessageBox::information(NULL, "Callback exemple", text);
}
int main(int argc, char **argv) {
QApplication application(argc, argv);
// Instantiate the viewer.
QGLViewer viewer;
// Restore the previous viewer state.
viewer.restoreStateFromFile();
// Create a scene, giving a pointer to the associated viewer.
Scene s(&viewer);
viewer.setWindowTitle("callback");
help();
viewer.show();
return application.exec();
}
</pre>
<p>
Back to the <a href="index.html">examples main page</a>.
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